This is primarily an investigation of two important regulatory processes in the replication of paramyxoviruses. One of these is the mechanism which determines the relative rates of synthesis of virus messenger RNA (transcription) and virus genomic RNA (replication). The other is the mechanism which specifies the abundance of each virus-specified polypeptide in infected cells. These mechanisms will be studied in infected cells and in cell-free systems, using biochemical methods to identify and characterize the relevant macromolecules. Temperature-sensitive mutants defective in critical functions will be used to relate in vitro to in vivo events. Another goal is to explore the structure of the paramyxovirus genome, using virus-specific messenger RNA species and subgenomic RNA species derived from defective-interfering (DI) particles. Methods will include RNA hybridization and electron microscopy.